Hmm. A sixth finger on his hand? A bit out there... a prosthetic, like a hearing aid, wooden leg, or glass eye? A fight to the death? One, and only one, appeal to a death sentence? I think there're lots of answers.

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There are three men in a boat with four cigarettes and no matches. How do they manage to smoke?

If one had a cigarette already lit, they could light off of it. Alternatively, they were struck by lightning and all caught on fire.

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What has four fingers and a thumb?

A person with one hand? A hand with a missing digit, because the thumb is a finger? Something hand-shaped, like a glove or a wooden hand?

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The man who builds it doesn't need it, the man who buys it doesn't use it, the man who uses it doesn't want it. What is it?

Heard this one.

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Why is a Raven like a writing desk?

Lewis Carroll never gave an answer, but there are a few good ones.

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I can travel around the entire world; all while staying in one corner. What am I?

Heard this one; my initial answer, "A person who is in a perpetual coma, sleeps in a corner bed, and is highly imaginative" was deemed too morbid.

Another of mine:

Errors we'll own to, if we're wise;What Gollum runs for exercise. (Hint: one word, six letters.)